Foiler Design

Done!

I'll contribute a section design for the hydrofoil. Any idea as to the all-up weight your'e shooting for and the speed range you want to cover?

 

Tom,
Thanks for beginning this thread.

As Moths are the only class which currently permits foil development, it makes sense to begin with Moth parameters.

The fully rigged Moth on the water is around 30Kg, plus the skipper, which in my case is 80Kg.

The latest Moths are using two Tee foils 800 x 120mm one on centreboard and the other on the rudder. These seem to take off in about 8-10 kts of wind they peak at about 18-22kts top speed.

This is about double the surface area Rich Miller uses on his sailboard, which is perhaps only 10 Kg lighter, so I think there is a big potential for them to improve a lot!

It occurs to me that there must be some good empirical information available from which we should be able to plot foil area against takeoff speed, takeoff windspeed and top speed.
Have you tried to do this or got any useful information?

My interest is to extrapolate the results and determine foil sizes necessary to give me the best combination of low take off speed and acceptable top speed. My feeling at present is that top speed is about 2.5 times take off speed, and that over 1200sqmm area will give a lower take off speed, but not much improvement in takeoff windstrength.

Any thoughts and data appreciated?

 

Would there be any merit in collaborative design of two differing styles of foiler - one a moth (someone like Ian Ward definitely knows more than I do about what is good for this class - hope he's right!) and the other an open development foiler, perhaps multihull based? How about a 16ft singlehander multi, or a 30 foot round the buoys multi, or a 40ft offshore racing (able to beat the 60's) multi? Any ideas?

Andy

 

Andy,
I have some ideas on applying the same principle to cats as well. I rather like a small one rather than big, as it is much lighter, cheaper and just as many thrills! Why not a 14ft single hander super light Cat? like a mini A!

Of course you can already buy a Rave or Trifoiler, so I am not sure if it is necessary to work on a multihull solution, except if you want a much simpler, cheaper version.

 

Retractable foils or?

In my opinion, whether it is a monohull or multihull, the central foiling issue ,from the standpoint of marketing a boat in the real world, is what do you do in lite air? There needs to be a design that allows the boat to make a smooth transition from being a "normal" sailboat to foiler w/o retrurning to the beach or having to carry a spare set of foils and capsizing the boat to put them on etc.
I believe to achieve general acceptance of a foiler as a concept it must sail very well in non foiling conditions as well as in foiling conditions. My company is about to introduce a 48" radio controled Bradfield type foiler with wand altitude control in which the foils retract in less than one second and deploy as quickly. In RC multihulls this solution is absolutely necessarry to race against others in the F48 class as well as to be able to market small multihulls in the first place. In model multihulls due to scale effect most of the natural pitch resistance is gone yet a foiler allows high speeds in all most conditions with no fear of capsize or pitchpole: an important concept in models where the skipper is on the shore. My current design still leaves the rudder T-foil down but it is a big improvement over the Rave type fixed foiler for models.(see the F3 at: www.microsail.com-our first foiler)
I 'm also working on a 16' foiler but without retractable foils so far.
I believe the biggest breakthru in foiler design will be a monohull and / multihull that can demonstrate exceptional performance on and off of foils and a virtually seemless transition between "modes".
I suggest a format here -because of the existing Sailing Dinghy design thread- that concentrates on a monohull foiler that meets the criteria of exceptional performance on and off foils. If we pick an International 14 we can sort of parallel the design input under the other thread giving essentially two teams working toward a high performance result in different directions.If we adopt the 14 type(using basically the 14 rules except those against foils--or just keeping the length the same?) as a primary focus it will be easy and VERY interesting to switch back and forth between threads to see how the designs are similar and how they are different. Then ,in the end if they build theirs and we build ours the result should be a triumph for anyone interested in foils and speed under sail! A sort of design competition between threads....

 

I would like to see the foiler designed as a Moth as if it looks to be viable, I would build it.
I have a question for Tom maybe, with Ian Wards Moth and the Miller windsurfer, the supercavitating foil at the bow would not carry any significant weight of the craft. Would such a foil be viable as the main foil to carry the majority of weight?
Supercavitating or sub cavitating.

 

john
from what i understand the supercavitating foil is only to track the surface. To do this it must of course provide some lift but this is very minimal when you look at how on the miller board he has to stand so far back. effectivley, it has the same function as the wand on your moths. only without the delay in the response that comes from the flexibility. it would be the equivalent of attaching the wand to the ruder foil so that it regulated pitch with height not lift.

essentially i thoguht that the main foil would always have to be a submerged lifting foil. in the miller article the canard he describes is the same size as the. this would suggest that for it to generate significant lift it would need very low wing loadings. ian also said (in the other thread) that the drag of a small super-cav foil was too much to use on his moth in light airs.

 

Astevo is correct.
The forward sensor foil is only touching the surface some of the time, it takes very little load, except momentarily in gusts. It presents surprisingly little drag.

Rich Miller says a supercavitating section is the best solition, and I agree with this, but I also need a boat to sail in light winds and so have compromised by using a standard aerofoil section.

Another big benefit of this, is that I can significantly increase the initial lifting foil area in lighter winds by moving my weight forward. This submerges the canard foil and it takes up to about half of the weight of the boat. Once I am up and going on the foils, I lean aft a little, the canard jumps free of the surface and I have effectively reduced the foil area in the water by 30%.

This gives some of the benefits of surface piercing foils which reduce wetted area as the speed increase, without the significant disadvantages of ventilation.

By using the canard this way, I believe it is not necessary to retract foils at all between light weather and foiling conditions!

If you need to retract anything then it is very easy to retract the canard. Especially in a scow as it sits snugly under the bow, completely out of the water flow.

I reckon you should think laterally! Use the main foil as a centreboard for displacement sailing and tilt it horizontally for foiling. This way you have just one foil, no need to retract it at all and you have a very simple transition control from displacement to foiling!

As for Skiff Moths I reckon it is really easy! Just put a fixed Tee foil on your centreboard and add a surface sensing canard at the bow... but don't forget to remove the Tee foil from your rudder...they are bad news!

ie: stick your Tee rudder in the centrecase..how simple is that!!.

 

ian
when you compromise with std section on the front do you loose the surface tracking behaviour that the s.c.foil has. we would all agree that the drag would be less this way but my feeling is that the forward foil should be there primarily to stay in contactwith the surface.

also if the 2 lifting points are the c/b and forward foil, does this mean that you have to sit a long way forward in order to stop falling over backwards. of course the rig will push the bow down a bit.

did you cut a big hole i the deck around the centre board to allow the rotation (or will you when you get the y foil built)?

 

G'day Astevo,
I think the aerofoil canard works fine and has good surface tracking properties.

I have an advantage over Rich Miller in that its angle of attack is easily adjustable, even while hiking. This means I can overcome some problems he found with the aerofoil buring itself at low angles of attack.

The whole thing balances nicely when I am in normal hiking position. (It was designed that way of course!) Moving my weight forward is really only a temporary transition from displacement sailing to foiling. I just lean forward, no need to move my ***!

If I lean too far aft, the canard never sees the water and I launch off into space with a crash soon after.. amazingly I can recover from this pretty easily. I have not experienced the Big crash Miller refers to because my canard is not fixed, if it catches water on the wrong side, it just pivots freely and does not drive the foil or boat under.

Yes, I have a hole in the deck, of course, but it is not as big as you may think.

 

I'll get to point now and describe what I was thinking of. The main foil (centreboard) could possibly be a super cavitating/sub cavitating section and the rudder could still have mild hydrofoil wing. No moving parts at all but it may only work in a breeze, a bit sailbaords prefer 12+ knots of wind for nice planing conditions.
All of this on a scow like hull might make nice machine if it were to work at all.

 

John,
It is a good idea and in principle could work, but I doubt it will be effective as the supercavitating foil is far less efficient, higher drag and perhaps half the lift of a submerged aerofoil.

The supercavitating foil is really best to retain flow at very hig speed and easily shed cavitation bubbles. Excellent for when you want to break the 45kt barrier, or for surface sensing, but not for surface load bearing.

 

I thought so but had to ask.
Ok then here's another. Same kind of design but a Tee type foiled centreboard with a flap. The flap control could be as is the control system on a dynafoil jet craft. The flap is spring loaded into the minimum lift position, at the water surface level on the same centre board (maybe 30-40cm from the hull) is a small horizontal fin like blade that trails on a pivot point. When this is in the water it pushes the flap via a rod to maximum lift, then when it breaks the surface the spring switches the flap to min lift. It's an on/off kind of system but all in the one foil without sensor arms or cables.
The rudder could possibly be with or without control flaps.
On second thought I think the dynafoil sensor just falls with gravity when above the water surface to reduce the flap angle, same but different. I imagine it should be possible to disengage the whole system for non foiling conditions to just have a trailing flap on the main foil.

 

Something like this:http://www.tspeer.com/Hydrofoils/generic.pdf?

 

For the project, I think a dinghy is best.

As for an offshore foiler, here's my latest thinking about a 36 ft racer/cruiser: